Generally, in a manufacturing process of a semiconductor device, photolithography is used to form a fine pattern. Multiple substrates called transfer masks are usually utilized in forming the fine pattern. In miniaturization of a semiconductor device pattern, it is necessary to shorten the wavelength of an exposure light source used in the photolithography, in addition to miniaturization of a mask pattern formed on the transfer mask. Shortening of wavelength has been advancing recently from the use of KrF excimer laser (wavelength 248 nm) to ArF excimer laser (wavelength 193 nm) as an exposure light source in the manufacture of semiconductor devices.
As for the types of the transfer mask, a half tone phase shift mask is known in addition to a conventional binary mask having a light shielding pattern made of a chromium-based material on a transparent substrate. Molybdenum silicide (MoSi)-based materials are widely used for a phase shift film of the half tone phase shift mask. However, as disclosed in Publication 1, it has been discovered recently that a MoSi-based film has low resistance to exposure light of an ArF excimer laser (so-called ArF light fastness). In Publication 1, ArF light fastness of a MoSi-based film is enhanced by subjecting the MoSi-based film after formation of the pattern under plasma treatment, UV irradiation treatment, or heat treatment to form a passivation film on a surface of the pattern of the MoSi-based film.
Publication 2 describes that the reason for low ArF light fastness of a MoSi-based film is instability of a transition metal in the film due to photoexcitation caused by irradiation of ArF excimer laser. Publication 2 applies SiNx, which is a material free of a transition metal, as a material forming a phase shift film. Publication 2 shows that, in the case of forming a single layer of SiNx film on a transparent substrate as a phase shift film, the composition of the SiNx film where optical properties required for the phase shift film can be obtained must be formed at unstable film-forming conditions (transition mode) in forming the film by reactive sputtering. To solve this technical problem, the phase shift film of Publication 2 has a stacked structure including a high transmission layer and a low transmission layer. Further, a SiN-based film formed in a poison mode region and having relatively high nitrogen content is applied to the high transmission layer, and a SiN-based film formed in a metal mode region and having relatively low nitrogen content is applied to the low transmission layer.